Electronic switching system for reducing noise transients

Abstract

A system for reducing noise transients in electrical carrier signals, carried simultaneously over two separate channels, that are identical in their program component but differ in transient noise content, comprising means for comparing noise transients in the respective channels and for transmitting the electrical sum of the two channels unless the noise transients of the two channels differ by more than a selectable threshold amount, in which case only the carrier signal with the lesser noise transient is transmitted.

What we claim is: 
     
       1. A system for controlling the transmission of electrical carrier signals according to the noise transients in a plurality of electrical carrier signals transmitted synchronously and simultaneously over separate channels, the carrier signals each including a corresponding program component and noise transients and the difference in the instantaneous magnitude of the signals being reflective of the difference in magnitude of their respective noise transients, said system comprising summing means operably connected to the channels for adding the electrical signals carried by said channels and for transmitting the added electrical signals;   switching means operably connected to the channels and actuable for disabling said summing means from transmitting said added electrical signals and for enabling the transmission of the electrical signal being transmitted in a portion of said channels and;   control means operably connected to the channels for comparing the instantaneous magnitudes of the electrical signals carried on the channels, and for actuating said switching means when the difference in magnitude of the respective noise transients of said signals exceeds a predetermined value.   
     
     
       2. The invention according to claim 1 wherein said separate channels are two in number, and said switching means comprise switches associated with each of said channels, said switches each having an open state, wherein the sum of the carrier signals in both channels is transmitted when the switches are both in the open state, and a closed state wherein a closed switch disables the summing means and enables the transmission of the carrier signal in the channel with which the switch is associated, said switches both being in the open state when the difference in magnitude of the noise transients of the electrical carrier signals in the channels at any time is below said predetermined level, and only the switch associated with the channel having the lesser noise transient level being in the closed state, when the difference in the magnitude of the noise transients in the respective signals at any time exceeds the predetermined level. 
     
     
       3. The invention according to either of claims 1 or 2 wherein said control means comprises threshold establishing means for establishing an electrical value definitive of said predetermined level. 
     
     
       4. The invention according to claim 2 wherein said channels have amplifier means for amplifying the respective input carrier signals, and gain control means electrically associated with one of said amplifiers for regulating the relative magnitudes of the input carrier signals. 
     
     
       5. The invention according to either of claims 1 or 2 and further including low frequency mixing means for equalizing the low frequency components of the electrical carrier signals in the respective channels, to render said control means responsive only to the portion of the respective carrier signals having frequencies above the low frequencies mixed by said low frequency mixing means. 
     
     
       6. The invention according to either of claims 1 or 2 wherein said control means comprises adding means for adding the carrier signals in the respective channels together to yield a combined signal reflective of the difference in magnitude between the respective carrier signals;   threshold establishing means for establishing predetermined voltage values;   comparing means connected to said adding means and to said threshold establishing means, and to said switching means, said comparing means comparing the combined signal at said adding means with said predetermined voltage values, and for generating output signals to actuate said switching means when said combined signal exceeds the predetermined voltage value with which the combined signal is compared.   
     
     
       7. The invention according to claim 2 and further including rectifying means associated with said first and second channels for rectifying the carrier signals in the respective channels to generate signals of opposite polarity in said channels; and adding means interconnecting said channels for adding the respective carrier signals to yield a combined signal with a value reflective of the difference in magnitude between the respective carrier signals; said switches being responsive to the magnitude of said combined signal. 
     
     
       8. The invention according to claim 1 wherein said switching means are actuable for enabling the transmission of the electrical signals being transmitted in that portion of said channels having the lowest noise transient level. 
     
     
       9. The invention according to claim 1 wherein said switching means are actuable for enabling the transmission of the electrical signals being transmitted in that portion of said channels having the greatest magnitude. 
     
     
       10. A system for controlling the transmission of electrical carrier signals transmitted synchronously and simultaneously over first and second channels, the carrier signals each including an identical program component and differing noise transients, and the difference in the instantaneous magnitudes of the carrier signals being reflective of the difference in their noise transients, said system comprising: first and second rectifying means connected in said first and second channels, respectively, for rectifying the carrier signals in the respective channels to generate a positive carrier signal in the first channel and a negative carrier signal in the second channel;   adding means interconnecting said channels for adding the respective carrier signals to yield a combined signal with a value reflective of the difference in magnitude between the respective carrier signals;   first and second voltage establishing means associated with the first and second channels for establishing first and second threshold voltages of opposite polarity, said voltage establishing means being connected to said adding means to generate a trigger signal when said combined signal exceeds either of said threshold voltages;   first and second comparators having negative and positive input ports respectively connected to the first and second channels, and positive and negative input ports connected to the respective first and second threshold means, one of said comparators generating a switching signal in response to the transmission of one of said trigger signals to said one comparator;   a summer comprising resistance devices connected to said first and second channels and to each other; and   first and second switches connected to said first and second comparators and being in low resistance lines shunting said respective resistance devices; said switches being normally open but closing in response to the generation of a switching signal by the comparator connected thereto;   said summer adding the carrier signals in the first and second channels to yield as an output the electrical sum of said carrier signals when the difference in the noise transient levels in the carrier signals is below said threshold values, and the one of said first and second switches receiving a switching signal from its associated comparator closing to yield as an output the carrier signal having the lower noise transient level when the difference in noise transient levels in the carrier signals exceeds the threshold values.   
     
     
       11. The invention according to claim 9 wherein the resistance devices of said summer meet at a first juncture and said switches are connected together at a second juncture, and wherein said system further includes output resistance means connected to said first and second juncture. 
     
     
       12. The invention according to claim 10 wherein the resistances of the resistance devices of said summer and of said output resistance means cause said devices and said output resistance means to yield an output signal with the same program component for input carrier signals having equal program components, when either or both of said switches are open. 
     
     
       13. The invention according to claim 2 and further including balance adjustment means for adjusting the program component of the two channels to equalize the program components of the respective carrier signals. 
     
     
       14. The invention according to claim 2, and further including balance adjustment means for equalizing the program components of the respective carrier signals in said first and second channels, said balance adjustment means comprising a unity-gain phase reversing amplifier connected in series in one of said channels. 
     
     
       15. The invention according to claim 9, and further including balance adjustment means for adjusting the program component of the two channels to equalize the program components of the respective carrier signals. 
     
     
       16. The invention according to claim 9, and further including balance adjustment means for equalizing the program components of the respective carrier signals in said first and second channels, said balance adjustment means comprising a unity-gain phase reversing amplifier connected in series in one of said channels.